This invention relates to a system for implosion protecting color television picture tubes and a method of assembly thereof. Conventionally, a color television picture tube has an evacuated glass bulb which includes a faceplate with a rearward flange and a funnel sealed to the faceplate flange along a planar sealing interface. The faceplate has a concave inner surface upon which is deposited a luminescent phosphor screen. Due to the high vacuum in the bulb, several tons of atmospheric pressure are exerted on the faceplate, causing the bulb to be susceptible to implosion. (The term "implosion"is defined by Underwriters Laboratory Incorporated as a "rapid and sudden inward bursting of a high-vacuum glass envelope.") It is of the utmost importance in the interest of safety to prevent the bulb from violently imploding should it be struck, for example, by a heavy missile.
There have evolved a number of approaches to implosion protecting color CRT's (cathode ray tubes) of the described type having a conventional bulb (with a flanged faceplate). One approach is implemented in systems referred to as "rimbond"systems. The rimbond system has a scalloped metal frame which surrounds the flange found on every conventional faceplate. A 3 small gap between the frame and the faceplate flange is filled with a cement--typically an epoxy resin. In a rimbond system, the frame is not under tension. The cement contains the glass shards of a shattered faceplate long enough to permit gradual (and therefore nonviolent) devacuation of the bulb. Exemplary U.S. Pat. Nos. illustrating rimbond systems are 3,485,407; 3,558,818; 3,412,203 and 3,835,250. A major drawback to rimbond systems has been the large amount of (very costly) epoxy cement required.
A second basic implosion protection approach is termed the "tension band"approach. Systems implementing this approach comprise a band which is placed around the face plate flange and put under very high tension. The tension band around the faceplate flange constricts the flange and, like the rimbond systems, holds the shards of a fractured faceplate in position until the bulb has gradually devacuated. Numerous patents have been issued on various aspects of tension band systems. See U.S. Pat. Nos. 3,818,557; 3,456,076; 3,556,306; 3,597,537; 3777,057; 3,845,530; and 3,890,464.
Another approach is to bond a transparent protective shield over the front surface of the faceplate. Systems following this approach are commonly termed "bonded panel" systems.
Yet another approach to implosion-protecting color CRT's with conventional faceplates involves using an expansible frame and a tension band to constrain the expansibility of the frame. The frame comprises an overlapped pair of "C"-shaped half frames. A viscous cement is typically applied to each of the half-frames; the half-frames are then placed around the faceplate flange with their ends overlapping. Before the cement has set, a tension band is drawn up tightly around the frame and faceplate flange. It is common to use a lighter weight tension band than is used in a pure tension band system.
A U.S. Pat. No. 3,647,960 -- Takemoto et al discloses still another implosion protection system for a color CRT of the type having a conventional bulb with a flanged faceplate. The implosion system of Takemoto et al comprises a series of closely spaced, mutually insulated turns of wire wrapped (with or without tension) around and adhered to the flange of the faceplate.
A U.S. patent to Powell et al -- 3,519,161 discloses the use of a limited number of turns of reinforcing wire around the flange of a color CRT faceplate of the conventional type to enhance the resistance of the tube to implosion.
U.S. Pat. No. 3,166,211--Stel et al discloses an implosion protection system for a CRT comprising a fiber-impregnated sheath on the exterior of the CRT bulb. In one embodiment, glass fibers are embedded in a cord which is wrapped around and bound to the exterior of a tube to provide implosion protection.
Yet another implosion protection system for a conventional CRT bulb is disclosed in U.S. Pat. No. 3,220,593 in which a webbing material is glued to a substantial portion of the funnel and to the faceplate flange. A tension band is applied around the flange of the faceplate and over the webbing material. Systems such at this have apparently not met the rigid test of commercial use; to my knowledge, no such system has found a practical application in the color television picture tube market. Other U.S. Pat. Nos. disclosing the use of a webbing material in an implosion protection system for a color CRT are 3,206,056 and 3,314,566.
This invention has exclusive application to a non-conventional color CRT bulb having a flangeless faceplate, as shown, e.g., in U.S. Pat. No. 3,912,963. The referent U.S. Pat. Nos. 4,037,255, 4,004,092, 4,016,364, 4,021,850, and 4,012,773, and copending application Ser. No. 718,631 discloses a number of predecessor implosion protection systems for a bulb of such character.
A U.S. Pat. No. 2,222,197 to Engels discloses a CRT in which the bulb comprises a flangeless faceplate inset in an expanded open end of a cooperating funnel. A band allegedly providing implosion protection surrounds the outside of the funnel near the open end thereof.